Power semiconductor modules are known in the art. Generally, power semiconductor modules comprise a baseplate, on which baseplate electrical conductors such as metallizations are provided which serve as a location for power semiconductor devices, or chips, respectively. Said chips are connected to terminals, such as control terminals. Further, additional circuit boards may be provided which are positioned in a distance from the power semiconductor devices and arranged above said power semiconductor devices. The above defined arrangement is generally located in a housing which is filled with an insulating gel, such as silicon gel.
Ultrasonic welding (US welding) is known in the power semiconductor industry for the welding of terminals to metalized ceramic substrate. The ultrasonic welding is advantageous in terms of reliability and production throughput when compared to traditional joining techniques such as soldering.
It is, however, known for such welding processes that small sized particles are ejected out from the joining partners by mechanical forces with high temperatures and velocity such, that they get embedded in or adhered on various building blocks used for the module packaging. Further particles are also scattered when the welding tool cleans itself using ultrasonic vibration. If the particle debris is not completely removed, they may trigger poor partial discharge properties and breakdown of electrical insulation especially at high voltages. Therefore, regarding ultrasonic welding, a primary challenge is to clean the metal particles generated during the welding process.
JP2010040615 A describes a semiconductor device which includes a wiring pattern formed on an insulating substrate, a semiconductor element mounted on the wiring pattern and a lead frame mounted on the wiring pattern by ultrasonic bonding. A resin is applied around the ultrasonic bonded lead frame. According to this document, scattering of scrap metal generated in connection of the substrate wiring with the external connection lead by ultrasonic bonding should be prevented.
However, an ultrasonic welding process still has potential for improvements in particular with regard to contamination due to scattered particles.